(4)Where a person, having contracted for the purchase of any property, but not having obtained a conveyance thereof, contracts to sell the whole, or any part thereof, to any other person or persons, and the property is in consequence conveyed by the original seller to different persons in parts, the conveyance of each part sold to a sub-purchaser shall be chargeable with ad valoremad valorem duty in respect only of the excess of the original consideration over the aggregate of the considerations paid by the sub-purchaser or the market value of the property, whichever is higher:Provided that the duty on such last-mentioned conveyance shall in no case be less than one hundred rupees.
